The present invention relates to a trimmer capacitor, as well as to a method of producing the same, and, more particularly, to a trimmer capacitor and a method of producing the same making use of a ceramic as the dielectric body, the ceramic being composed mainly of titanium dioxide.
Trimmer capacitors having dielectric bodies composed mainly of ceramic are known. These trimmer capcitors are produced by a process as summarized below. Namely, a stator electrode, ceramic dielectric body and a rotor electrode are formed in layers on an insulating frame formed from a material such as plastic. A rotor shaft extends through the rotor electrode, ceramic dielectric body, and the stator electrode, and is carried rotatably by the frame. The rotor electrode and the ceramic dielectric body are fixed to the rotor shaft for rotation unitarily with the latter relative to the stator electrode. As the rotor shaft is rotated, the overlapping area of the rotor electrode and the stator electrode is changed to vary the capacitance.
A ceramic mainly composed of titanium dioxide (TiO.sub.2) is preferred as the material for the dielectric body of the trimmer capacitor of the type described since it exhibits a specific dielectric constant which is practically about 10 to 1000 times as large as those of other ceramics and plastic films, and also has other superior electric characteristics. This ceramic, however, has only a small flexibility and is mechanically fragile. The mechanical defect is increased if barium titanate (BaTiO.sub.2) is used for attaining a higher dielectric constant.
More specifically, the rotor electrode of the conventional trimmer capacitor of the type described is fabricated by applying in a substantially semi-circular pattern is silver paste or the like electrode material to a thin disc of ceramic which is inherently very fragile. In addition, the rotor electrode which is rotated together with the ceramic dielectric body is liable to be subjected to impacts. Thus, the thickness of the ceramic dielectric body may be reduced to an order of about 0.3 mm only. For those reasons, it has been extremely difficult to obtain a small-sized and high-performance trimmer capacitor having a high capacitance and wide range of capacitance.